To read sensitive settings from the environment variables, perform these steps:

1. At the beginning of settings/_base.py, define the get_secret() function as follows:

# settings/_base.py
import os
from django.core.exceptions import ImproperlyConfigured

def get_secret(setting):
    """Get the secret variable or return explicit exception."""
    try:
        return os.environ[setting]
    except KeyError:
        error_msg = f'Set the {setting} environment variable'
        raise ImproperlyConfigured(error_msg)

2. Then, whenever you need to define a sensitive value, use the get_secret() function, as shown in the following example:

SECRET_KEY = get_secret('DJANGO_SECRET_KEY')

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': get_secret('DATABASE_NAME'),
        'USER': get_secret('DATABASE_USER'),
        'PASSWORD': get_secret('DATABASE_PASSWORD'),
        'HOST': 'db',
        'PORT': '5432',
    }
}